SiCOH film preparation using precursors with built-in porogen functionality

ABSTRACT

A method of fabricating a dielectric material that has an ultra low dielectric constant (or ultra low k) using at least one organosilicon precursor is described. The organosilicon precursor employed in the present invention includes a molecule containing both an Si—O structure and a sacrificial organic group, as a leaving group. The use of an organosilicon precursor containing a molecular scale sacrificial leaving group enables control of the pore size at the nanometer scale, control of the compositional and structural uniformity and simplifies the manufacturing process. Moreover, fabrication of a dielectric film from a single precursor enables better control of the final porosity in the film and a narrower pore size distribution resulting in better mechanical properties at the same value of dielectric constant.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/329,560, filed Jan. 11, 2006 now U.S. Pat. No. 7,521,377. The presentapplication is related to co-assigned U.S. application Ser. No.10/964,254, filed Oct. 13, 2004, entitled “ULTRA LOW k PLASMA ENHANCEDCHEMICAL VAPOR DEPOSITION PROCESSES USING A SINGLE BIFUNCTIONALPRECURSOR CONTAINING BOTH A SiCOH MATRIX FUNCTIONALITY AND ORGANICPOROGEN FUNCTIONALITY”, now U.S. Pat. No. 7,491,658 the entire contentsof which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to a method of fabricating adielectric material that has an ultra low dielectric constant (or ultralow k) using at least one organosilicon precursor. The organosiliconprecursor employed in the present invention includes a moleculecontaining both an Si—O structure and a sacrificial organic group, as aleaving group. The use of an organosilicon precursor containing amolecular scale sacrificial leaving group enables control of the poresize at the nanometer scale, control of the compositional and structuraluniformity and simplifies the manufacturing process. Moreover,fabrication of a dielectric film from a single precursor enables bettercontrol of the final porosity in the film and a narrower pore sizedistribution resulting in better mechanical properties at the same valueof dielectric constant.

BACKGROUND OF THE INVENTION

The continuous shrinking in dimensions of electronic devices utilized inultra large scale integrated (ULSI) circuits in recent years hasresulted in increasing the resistance of the back-end-of-the-line (BEOL)metallization as well as increasing the capacitance of the intralayerand interlayer dielectric. This combined effect increases signal delaysin ULSI electronic devices. In order to improve the switchingperformance of future ULSI circuits, low dielectric constant (k)insulators, particularly those with a dielectric constant significantlylower than silicon oxide, are needed to reduce the capacitances.Dielectric materials (i.e., dielectrics) that have low k values arecommercially available. Most commercially available dielectricmaterials, however, are not thermally stable when exposed totemperatures above 300° C. Integration of low k dielectrics in presentULSI chips requires a thermal stability of at least 400° C.

The low k materials that have been considered for applications in ULSIdevices include polymers containing atoms of Si, C, O and H, such asmethylsiloxane, methylsilsesquioxanes, and other organic and inorganicpolymers. For instance, an article by N. Hacker et al. “Properties ofnew low dielectric constant spin-on silicon oxide based dielectrics”Mat. Res. Soc. Symp. Proc. 476 (1997): 25 describes materials thatappear to satisfy the thermal stability requirement, even though some ofthese materials propagate cracks easily when reaching thicknesses neededfor integration in an interconnect structure when films are prepared bya spin-on technique.

The ability to fabricate a low k material by either a spin-on or aplasma enhanced chemical vapor deposition (PECVD) technique is anadvantage. Despite the numerous disclosures of low k dielectricmaterials, there is a continued need to improve the properties of thesematerials. For example, a SiCOH dielectric material having a lowerinternal stress, improved thermal stability, lower cost, nanometer scalepore size, narrow distribution of pore size, homogeneous poredistributions throughout the film thickness, and better process controlwithin processing temperatures used in current ULSI technologies are allneeded.

It is commonly found when making SiCOH dielectrics by conventionalspin-on techniques using various chemistries that the final film has apore size distribution that is broader than desired, and often includespores larger than 2 nm diameter.

It is also commonly found that SiCOH dielectrics made in the prior artfrom two or more separate organosilicon and/or porogen molecules are notuniform in atomic and structural composition, both when measured acrossthe substrate diameter, and through the depth of the dielectric layer.The use of 300 mm Si wafers has made this problem of chemical uniformityacross the wafer more pronounced.

Additionally, prior art CVD SiCOH dielectrics made from two or moreseparate organosilicon and/or porogen molecules were found to exhibitprocess variation or process instability due to small changes in theflow rate of one of the two precursors, known to those skilled in theart as drift in the flow rate. Moreover, prior art SiCOH dielectricsmade from two or more separate organosilicon and/or porogen molecules ina PECVD process have been found to have a small component of largerpores due to the formation of dimers or trimers of the porogen in thePECVD reactor.

In view of the above, there is a need to provide a process to fabricatea layer of a SiCOH dielectric having improved film properties, that hasan easily controlled, narrow, pore size distribution, and is uniform inatomic and structural composition, both when measured across thesubstrate diameter, and through the depth of the layer, which does notexhibit any variation in the process or process instability.

SUMMARY OF THE INVENTION

The present invention provides a method for fabricating a porousdielectric material of the general composition SiCOH having a dielectricconstant of not more than about 2.7 from at least one organosiliconprecursor containing a built-in sacrificial organic porogen. In apreferred embodiment of the present invention, a single organosiliconprecursor containing a built-in sacrificial organic porogen is employed.Both a spin-on embodiment and a PECVD embodiment are described in thepresent application.

As to be described in greater detail herein below, the built-insacrificial organic porogen is a functional group that is present andcovalently bound to the preliminary film skeleton, which is subsequentlyremoved by an energetic treatment step. As such, the porogen employed inthe present invention is not present in the dielectric film. Instead,pores (e.g., voids) are present in the dielectric film after theenergetic treatment step, which renders the dielectric film porous.Preferably, the dielectric constant of the dielectric material of thepresent invention is from about 1.5 to about 2.6, and most preferably,the dielectric constant is from about 1.8 to 2.5. All dielectricconstants mentioned in the present application are relative to a vacuum,unless otherwise specified. Because the inventive dielectric film has ak that is not more than 2.7, it can be referred to as an ultra low k(ULK) dielectric.

Specifically, the present invention provides methods for fabricating aporous SiCOH dielectric comprising Si, C, O and H atoms using depositionof a preliminary film and an energetic treatment to transform thepreliminary film into a porous ULK dielectric film.

More specifically, the present invention describes methods forfabricating a layer of a SiCOH dielectric material having improved filmproperties, which is uniform in atomic and structural composition, bothwhen measured across the substrate diameter, and through the depth ofthe layer, that does not exhibit variation in the process or processinstability. Further, the dielectric films of the present invention havea pore size on the nanometer scale without the presence of larger pores,and hence the distribution of pores sizes is uniform and narrow.

The use of the inventive methods with deposition of a preliminary filmfrom one or more, preferably a single, organosilicon precursorscontaining a built-in sacrificial organic porogen enables better controlof the porosity in the final film and a narrower pore size distribution,resulting in better mechanical properties at the same values ofdielectric constant. Furthermore, the deposition of a preliminary filmfrom the organosilicon precursors described herein enables improvedmechanical properties of the final SiCOH dielectric film.

By “improved mechanical properties” it is meant that the final porousdielectric film formed from the method of the present invention has atensile stress of less than 60 MPa, an elastic modulus from about 2 toabout 15 GPa, and a hardness from about 0.2 to about 2 GPa as determinedby nanoindentation techniques. The stress value is measured by measuringthe curvature of a substrate both with, and without, the film depositedon said substrate, and using the change in curvature to calculate thestress. Tools operating on this principle are well known in the art. Themodulus is commonly measured by nanoindentation on a film of 1 micronthickness, or greater. Other methods to measure the modulus are lesscommon, for example surface acoustic wave spectroscopy (SAWS).

In broad terms, the method of the present invention comprises:

providing at least one organosilicon precursor containing a built-insacrificial organic porogen, where said at least one organosiliconprecursor with the built-in sacrificial organic porogen is selected fromsilane (SiH₄) derivatives having the molecular formula SiR*R¹R²R³,disiloxane derivatives having the molecular formulaR*R⁵R⁶Si—O—Si—R⁷R⁸R⁹, trisiloxane derivatives having the molecularformula R*R¹¹R¹²—Si—O—Si—R¹³R¹⁴—O—Si—R¹⁵R¹⁶R¹⁷ and disilaalkanederivatives having the molecular formula R*R⁵R⁶Si—(CH₂)_(n)—Si—R⁷R⁸R⁹,where n equals 1-2, R* is a sacrificial organic porogen group, andR¹⁻¹⁷, which may or may not be identical, are selected from H, alkyl,alkoxy, epoxy, phenyl, vinyl, allyl, alkenyl or alkynyl groups that maybe linear, branched, cyclic, polycyclic and may be functionalized withoxygen, nitrogen or fluorine containing substituents;forming a preliminary dielectric film containing said at least oneorganosilicon precursor with the built-in sacrificial organic porogen ona surface of a substrate from the vapor or liquid phase; andperforming an energetic treatment step on said preliminary dielectricfilm to substantially remove said built-in sacrificial organic porogenfrom said preliminary dielectric film providing a porous dielectric filmcomprising atoms of Si, C, H and O that has a dielectric constant ofabout 2.7 or less and a uniform and narrow and uniform pore sizedistribution.

According to the present invention, the sacrificial organic porogengroup R* is selected from a branched alkyl including, for example,tertiary-butyl, branched alkoxy including, for example, tertiary butoxy,cyclic alkyl, cyclic alkoxy, aldehydes, ketones, esters, thioesters,amines, urethanes, triphenyl, alkyl phenyl carbinyl, substituted allyl,cyclohepatrienyl, cyclopropyl carbinyl, nitrites, azo derivatives, andalkyl groups which are connected to Si by a linker group. The linkergroup, which is connected to silicon, may itself bethermally/photochemically labile or provide a platform to which labilesubstituents can be attached (e.g., hydroxyethyl, hydroxypropyl,aminoethyl, aminopropyl, carboxyethyl, carboxypropyl, branchedfunctional tethers, etc). Typically, the linker functionality will besensitive to heat, light, ionizing radiation, or catalytic reagentsgenerated as above. Preferably, the sacrificial porogen group R* isselected from a branched alkyl, cyclic alkyl, branched alkoxy, cyclicalkoxy, aldehydes, ketones, esters, thioesters, amines, urethanes,nitrites, azo derivatives, triphenyl, cycloheptatrienyl and alkyl groupswhich are connected to Si by the linker group. Alternatively, the labilegroup may be directly bonded to silicon without a linker group (e.g.,branched alkoxy, etc.) such that the alkyl substituent is removed upontreatment leading to a silanol, which undergoes subsequent condensationinto the final film.

In accordance with the present invention, the preliminary film containsa functional group selected from the group consisting of branched orcyclic hydrocarbon groups, polycyclic hydrocarbon groups, branched orcyclic hydrocarbon groups bonded between two or more Si atoms,polycyclic hydrocarbon groups bonded between two or more Si atoms, acylgroups, ester groups, xanthate groups, amines, amine oxides, ethers,sulfonyl, sulfinyl, phosphate, phosphonyl, phosphinyl, organometallicand borate groups.

In accordance with the present invention, the energetic treatment stepreleases molecules from the preliminary film that are selected from thegroup consisting of linear or cyclic hydrocarbon fragments, olefins,acetylenes, alcohols, organic acids, amides, vinyl esters, xanthates,thioacids, amines, hydroxylamines, phosphines, phosphoric acids,phosphoric esters, substituted phosphonic, phosphinic esters, sulfonicacids, sulfinic acids, sulfides, mercaptans, nitrites and borates, andsmaller fragments of these functional groups.

In a preferred embodiment of the present invention, the at least oneorganosilicon precursor containing a built-in sacrificial organicporogen has molecules of the following basic formulas;

wherein at least one of A, B or ring is R* as described above, andwherein ring further is either one hydrocarbon ring containing a C—Cunit bonded between two Si atoms or a polycyclic structure containing aC—C unit between two Si atoms. It is noted that these formulas aregeneric to those shown in Schemes 1-5 below. Within the invention, oneR* group may be present on one Si atom, or there may be two R* groups ontwo Si atoms.

According to this invention, the energetic treatment step may use one ormore of light, ionizing radiation, thermal energy or the generation of acatalytic species, and the R* substituents are essentially removed inthis step to produce nanometer scale porosity in the final film.

In addition to the method described above, the present invention alsoprovides a SiCOH dielectric film which is prepared using the methoddescribed above. Specifically, the dielectric film of the presentinvention comprises a dielectric material comprising atoms of Si, C, Oand H, said dielectric material having a covalently bondedtri-dimensional network structure, a dielectric constant of not morethan 2.7, a controlled porosity having molecular scale voids from about0.3 to about 20 nanometers in diameter, and preferably from about 0.3 toabout 5 nm in diameter. According to the invention, the molecular scalevoids occupy a volume of between about 5% and about 60%.

Also according to the invention, the dielectric material containsnanometer or molecular scale pores (voids) that are characterized by apore size distribution (PSD), which has a maximum. The maximum sizedistribution is the most common pore size, and it is typically about 1-2nanometers. More generally, the maximum size of the pores is from about0.1 to 10 nanometers, with 0.3 to 3 nanometers being preferred. Theremoval of the R* group produces this porosity called here “nanometerscale porosity”. The PSD is measured with characteristic dimensions innanometers.

The at least one dielectric film comprising the inventive SiCOHdielectric may comprise an interlevel and/or intralevel dielectriclayer, a capping layer, and/or a hard mask/polish-stop layer in anelectronic structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the measured pore sizedistribution of the films of the present invention.

FIG. 2 is a pictorial representation illustrating the basic processingsteps of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides a method of fabricating a porousULK dielectric film having a uniform and narrow pore size distributionutilizing at least one organosilicon having a built-in sacrificialorganic porogen, will now be described in greater detail by referring tothe following discussion as well as the drawings that accompany thepresent application.

As stated above, the present invention provides a method of fabricatinga porous ULK dielectric film which includes first providing at leastone, preferably a single, organosilicon precursor containing a built-insacrificial porogen, where said at least one organosilicon precursorwith the built-in sacrificial organic porogen is selected from silane(SiH₄) derivatives having the molecular formula SiR*R¹R²R³, disiloxanederivatives having the molecular formula R*R⁵R⁶Si—O—Si—R⁷R⁸R⁹,trisiloxane derivatives having the molecular formulaR*R¹¹R¹²—Si—O—Si—R¹³R¹⁴—O—Si—R¹⁵R¹⁶R¹⁷ and disilaalkane derivativeshaving the molecular formula R*R⁵R⁶Si—(CH₂)_(n)—Si—R⁷R⁸R⁹, where n is1-2, R* is a sacrificial porogen group and R¹⁻¹⁷, which may or may notbe identical, are selected from H, alkyl, alkoxy, epoxy, phenyl, vinyl,allyl, alkenyl or alkynyl groups that may be linear, branched, cyclic,polycyclic and may be functionalized with oxygen, nitrogen or fluorinecontaining substituents. In one highly preferred embodiment, theorganosilicon precursor includes a 1,3-disilapropane derivative suchthat the resultant film formed after energetic treatment includesSi—CH₂—Si bonding units.

The term “alkyl” is used herein to denote a paraffinic hydrocarbon grouphaving the formula —C_(n)H_(2n+1) where n is an integer of 1 or greater,preferably n is from 1 to 16. Examples of such alkyls include, but arenot limited to: methyl, ethyl, butyl, propyl, and the like includingbranched and cyclic systems.

The term “alkoxy” is used herein to denote a compound having the formula—OR, wherein R is an alkyl group as defined above. Examples of suchalkoxys include, but are not limited to: methoxy, ethoxy, butoxy,propoxy and the other like compounds including carbon-branched andcyclic.

The term “epoxy” is used herein to denote an organic compound containinga reactive group resulting from the union of an oxygen atom with twocarbon atoms. Examples of such epoxies include, but are not limited to:ethylene oxide.

The term “phenyl” group is used herein to denote a —C₆H₅ group that isderived from benzene. Also included would be alkyl or alkoxy substitutedbenzene derivatives including those with multiple substitution.

The term “vinyl” is used herein to denote a compound having a CH₂—CH—group. Examples include vinyl chloride, vinyl acetate, styrene, methylmethacrylate and acrylonitrile.

The term “allyl” is used in the present application to denotes acompound having a CH₂═CHCH₂— group. Examples include allyl chloride,allyl bromide, allyl amine, allyl alcohol, allyl acrylate, allyl acetoneand the like.

The term “alkenyl” denotes a compound including a saturated group havingthe formula —C_(m)H_(2m) wherein m is an integer of 2 or greater,preferably m is from 2 to 20. Examples, include, but are not limited to:ethylene, propylene, butylene and the like.

The term “alkynyl” denotes a compound a paraffinic compound thatincludes at least one —C≡C— bond. Examples include, but are not limitedto: ethynyl, propynyl, 1-butynyl, 1hexyne, 3-hexyne, and the like.Diynes and triynes are included within the definition of an alkynyl.

According to the present invention, the sacrificial organic porogengroup R* is selected from a branched alkyl including, for example,tertiary-butyl, branched alkoxy including, for example, tertiary butoxy,cyclic alkyl, cyclic alkoxy, aldehydes, ketones, esters, thioesters,amines, urethanes, triphenyl, alkyl phenyl carbinyl, substituted allyl,cyclohepatrienyl, cyclopropyl carbonyl, nitriles, azo derivatives, andalkyl groups which are connected to Si by a linker group. The linkergroup, which is connected to silicon, may itself bethermally/photochemically labile or provide a platform to which labilesubstituents can be attached (e.g., hydroxyethyl, hydroxypropyl,aminoethyl, aminopropyl, carboxyethyl, carboxypropyl, branchedfunctional tethers, etc.). Typically, the functionality bound by thelinker group will be sensitive to heat, light, ionizing radiation, orcatalytic reagents generated as above. Preferably, the sacrificialporogen group R* is selected from branched alkyl, cyclic alkyl, branchedalkoxy, cyclic alkoxy, aldehydes, ketones, esters, thioesters, amines,urethanes, nitrites, azo derivatives, triphenyl, cycloheptatrienyl andalkyl groups which are connected to Si by the linker group. The labilegroup may be directly bonded to silicon without a linker (e.g., branchedalkoxy, etc.) such that the alkyl substituent is removed uponthermal/photochemical treatment leading to a silanol that undergoessubsequent condensation into the matrix. In this regard, it may beadvantageous to exchange some of the methoxy/ethoxy substituents in thesol-gel precursor with bulky alkoxy substituents which are not easilyhydrolyzed (tertiary alkoxy, isopropoxy, neopentoxy, fenchyloxy,5-norbornenyloxy, etc.) but are thermally labile or are labile to lightor ionizing radiation or catalytic species generated therein (e.g. acidor base).

A preliminary dielectric film is then formed on a surface of a substrateby introducing the at least one organosilicon precursor with thebuilt-in sacrificial organic porogen into a reactor including thesubstrate. After the preliminary dielectric film is formed, an energetictreatment step is performed to substantially remove said built-inporogen from the preliminary dielectric film. Thus, a porous dielectricfilm comprising atoms of Si, C, H and O that has a dielectric constantof about 2.7 or less and a uniform and narrow pore size distribution isformed after the above steps have been performed.

Specifically, a porous SiCOH dielectric material having improved filmproperties, which is uniform in atomic and structural composition, bothwhen measured across the substrate diameter, and through the depth ofthe layer, that does not exhibit variation in the process or processinstability is provided. Further, the dielectric films of the presentinvention have a pore size on the nanometer scale without the presenceof larger pores, and hence the distribution of pores sizes is uniformand narrow.

By “uniform in atomic composition”, it is meant that the dielectricmaterial of the present application has a substantially constantdistribution of atoms throughout the film in both the vertical andhorizontal direction. By “uniform in structural composition”, it ismeant a substantially constant arrangement of atoms within the film inboth the vertical and horizontal directions. By “uniform and narrow” itis meant that the distribution of pores sizes does not contain a largediameter tail. Referring to FIG. 1, the curve labeled 1 is the PSD ofthe majority fraction of the pores of the inventive porous dielectricmaterial, and the cross-hatched area under Curve 1 is labeled 2, and isthe fraction of the pores having a diameter of less than 1 nm. Thecomponent of pores larger than 1 nm is labeled 4 for a typical materialof the prior art, and the component of pores larger than 1 nm for thedielectric material in accordance with one of the embodiments is labeled3. The component of pores larger than 1 nm for a preferred material ofthe present invention is the dashed line labeled 5.

In a preferred treatment, the substrate containing the film depositedaccording to the above process is placed in an ultraviolet (UV)treatment tool, with a controlled environment (vacuum or reducingenvironment containing H₂, or an ultra pure inert gas with a low O₂ andH₂O concentration). A pulsed or continuous UV source may be used, asubstrate temperature of 300°-450° C. may be used, and at least one UVwavelength in the range of 170-400 nm may be used. UV wavelengths in therange of 190-300 nm are preferred within the invention.

Within the invention, the UV treatment tool may be connected to thedeposition tool (“clustered”), or may be a separate tool. Thus, as isknown in the art, the two process steps will be conducted within theinvention in two separate process chambers that may be clustered on asingle process tool, or the two chambers may be in separate processtools (“declustered”).

The present invention contemplates embodiments where spin-on coating isemployed in forming the preliminary dielectric film and embodimentswhere PECVD is employed in forming the preliminary dielectric film.Details of these various embodiments of the present invention will bedescribed in greater detail herein below.

The term “substrate” as used throughout the present application denotesa semiconductor material, an insulating material and/or a conductivematerial. The “and/or” designation means that combinations andmultilayers of these materials can be present in the substrate. Examplesof semiconductor material include Si, SiGe, SiC, SiGeC, InAs, InP, Gealloys, GaAs, silicon-on-insulators (SOIs), SiGe-on-insulators (SGOIs)and other like materials that exhibit semiconducting properties.Examples of insulating materials include inorganic dielectrics such as,for example, SiO₂, Al₂O₃, Ta₂O₅, TiO₂, LaO₂ and perovskite-type oxides,as well as organic dielectrics such as, for example, polyimdes,organosilanes, carbon doped oxides, and polyarylenes. Examples ofconductive materials include, for example, metals, metal silicides,metal nitrides and alloys thereof.

According to the invention, the steps of FIG. 2 are followed. Referringto FIG. 2, in Step 1, the organosilicon precursor molecule contains asubstituent R* that is thermally labile, or that may be decomposed bylight, ionizing radiation or the generation of catalytic species. InStep 2, a preliminary film is formed containing the R* groups. Formationof the preliminary film may include formation of a prepolymer bysolution phase chemistry. The prepolymer is then coated on a substrateand solvent is removed to form the preliminary film. Other methods toform the preliminary film are also described within the invention. InStep 3, the R* substituents are removed in the energetic treatment step.

The final dielectric film contains nanometer scale porosity that isformed by removal of the R* groups. Herein, the labile/decomposablesubstituents R* are called a “built-in sacrificial organic porogen”. Inone preferred embodiment, the precursor molecule also contains acombination of Si—CH₂—Si and Si—O bonds that will form the skeleton ofthe final dielectric film. In another preferred embodiment, thedielectric film includes Si—CH₂—CH₂—Si bonding units.

The preliminary film in Step 2 may be deposited using any depositionmethod, for example spin-on coating, plasma enhanced chemical vapordeposition (PECVD), thermal chemical vapor deposition, evaporation, orother methods.

In Step 3, energy is applied to the preliminary film in the form ofthermal energy, UV light, microwave, electron beam, ion beam or otherenergy source, such as a catalytic species. In some embodiments, acombination of two or more of these energy sources is employed. Thethird step described in FIG. 2 transforms the preliminary film into thefinal porous dielectric film. Specifically, during the third step theremoval of the R* group from the previously formed film produces aporosity with a characteristic dimension measured in nanometers, calledhere “nanometer scale porosity”. When the pore size distribution ismeasured for the final dielectric film, the maximum in the sizedistribution (most common pore size) is generally about 1 nanometer, andmay be from about 0.1 to 10 nanometers, with 0.3 to 3 nanometers beingpreferred.

The conditions for UV treatment were previously mentioned herein above.The following conditions for the other energetic treatment steps can beemployed in the present invention:

Thermal treatment—The thermal treatment may be performed by applyingheat to the substrate that includes the preliminary dielectric film.Typically, the temperature of thermal treatment is from about 300° toabout 350° C., with a temperature from about 350° to about 450° C. beingeven more typical. The time of thermal treatment various depending onthe type of thermal process used. The thermal process may include afurnace anneal, a rapid thermal anneal, a laser spike anneal, or a laseranneal. The thermal treatment may be performed under vacuum, or in aninert gas atmosphere such as, for example, He, Ar or N₂. Under somecircumstances the anneal may be performed in an oxidizing (air, CO, CO₂,etc.) or reducing (H₂, NH₃, etc.) atmosphere.

Electron Beam—The electron beam treatment is performed utilizing a toolthat is capable of heating the substrate to 300° to 500° C. andgenerating a uniform electron beam over the entire substrate. This tooloperates in vacuum, with electron beam energies in the range of 0.5 to10 keV (typically 1 to 5 keV) and total beam current in the range of 0.5to 10 milliAmperes, typically 1-5 milliAmperes. To treat the film, adose of 50 to 500 microCoulombs/cm² is typically used.

Catalytic Species—A catalytic species such as a supported or unsupportedmetal catalyst such as, for example, Pt, Pd, Ni, Rh, Cu, Al and the likecan be used in removing the sacrificial organic porogen from thepreliminary deposited dielectric film. In these cases, the metal is onthe substrate perhaps as defined patterns. The film is transformed intoa porous material in those regions contacting the metal at temperaturesabove 300° C. Alternatively a chemical catalyst produced from a thermalor photoacid generator (Bronsted or Lewis) or thermal or photobasegenerator (Lewis or Bronsted) may be used. The photoacid or photobasegenerator is incorporated into the dielectric formulation to beliberated after the film has been deposited and partly cured. Thecatalytic species assists in the removal of the porogen bonded to thesilicon-containing species. Similarly the acid or base generators couldbe sensitive to low valent metal (see above) and be decomposed toproduce the catalytic species in those regions where the films come intocontact with the metals.

Within all embodiments of the present invention, the chemistry shown isexemplary and related molecules with the same essential features may beused within the invention.

Within some embodiments of the present invention, the prepolymericsolution is processed by sol-gel hydrolysis, coating and thermal curing.This hydrolysis/condensation process may be done using water and acid inthe initial stages to form SiOH functionality. Within these embodiments,the presence of catalytic acid assists in the reaction. The presence ofacid also facilitates the SiOH condensation to produce siloxanecrosslinks. In the examples that use t-butoxy as the R* group, thet-butyl ether serves both as a source of SiOH in a nonaqueousenvironment and as a source of the pore generator.

The first embodiment of the present application describes the use of aspin-on dielectric film that utilizes an organosilicon precursor with abuilt-in porogen. Specifically, a multifunctional, polymerizableorganosilicon precursor is employed in this embodiment and it is appliedto a surface of a substrate. In the first embodiment, referring toScheme 1 below, sol gel chemistry which is well known in the art is usedto generate a prepolymer before coating the prepolymer on the substrate.Within this invention, a key feature is the ability to form prepolymersand condensable oligomers under conditions where thermally labilesubstituents and photoactive groups, which make up the group R*, areretained in the film. The sacrificial organic porogen substituents R*are then removed in the later energetic treatment step to produceporosity controlled on the nanometer scale under conditions where thecarbon linkages bridging silicon are retained. The sacrificial groupsmay be contained within the condensing alkoxy substituents or on othersubstituents bound to silicon.

Referring to Scheme 1, R=alkyl R₁ and R₂ may be alkyl, aryl, or alkoxy,R₃ may be hydrogen, alkyl, aryl, cycloalkyl or alkoxy and R₄ may bealkyl, aryl or alkoxy. Moreover, the reactions are shown to provide aroute to polymerizable precursors where the silicon substituents areseparated by a two-carbon bridge (Si—CH₂—CH₂—Si bonding unit). At thetop of Scheme 1 are example starting materials within the firstembodiment. These molecules are substituted derivatives of disilane.Shown at the top of Scheme 1 are highly substituted disilanederivatives, but related molecules with fewer alkoxy (OR) substituentsmay be used within the invention. Fluorine and chlorine substituents arealso acceptable for the subsequent oxidative addition. The startingmaterial may be symmetrical or unsymmetrical. A preferred substituent isalkoxy and most preferably multiple alkoxy substituents as shown at thetop of Scheme 1 are used. The disilane bond is prone to oxidativecleavage and addition to Pi bonds in the presence of various metalcatalysts (Pd, Pt, Rh, etc). Thus, within this invention, the units ofthe disilane are added across double bonds of olefins and allenes (shownin Scheme 1A), or across acetylenes (shown in Scheme 1B). This additioncan be quite stereospecific (i.e., Z) in the case of addition toacetylenes. In the case of acetylenes and allenes, unsaturation isretained. An example using an acetylene derivative is shown in Scheme1B. The unsaturation may be removed by hydrogenation if desired (videinfra) or it may be used intact to provide backbone crosslinking sitesupon further processing. Depending on the nature and number of alkoxysubstituents originally present, cyclic polymeric materials may also beproduced upon sol gel condensation. In this regard, the hydrolysis ofcyclic materials such as (33) leads to rapid cyclization, particularlyin dilute solution.

Suitable solvents in which to perform the reactions shown in FIG. 1include toluene, xylene, THF, glyme, diglyme and the like. The reactionsshown in FIG. 1 are carried out at a temperature from about 75° C. toabout 140° C., with a reaction temperature from about 90° C. to about130° C. being more preferred. Oxidative addition to olefins has beendescribed using zero valent platinum (T. Hayashi et al Organometallics1990, 9, 280). Low-valent palladium catalysts apparently do not work inoxidative addition to olefins. An alternative route to vicinal disilylsubstituted alkanes is available through the platinum catalyzedhydrosilation of substituted vinyl silanes with various hydridosilanemonomers (W. A. Piccoli et al J. Am. Chem. Soc. 1960, 82, 1883). Variouslow-valent palladium complexes are successful in promoting oxidativeaddition to acetylene and substituted acetylenes (H. Watanabe et al J.Organomet. Chem. 1981, 216, 149).

In these cases, one of the double bonds is retained and thestereochemistry is predominately Z. The olefins so obtained may bereduced using H₂ and Pd/C to produce the saturated derivative, if sodesired (K. Rahumian et al Chem. Mater. 2005, 17, 1529).

The reactions of Scheme 1 provide a route to polymerizable precursorswhere the silicon substituents are separated by a two-carbon bridge, andthese precursors are shown as item (31) and (33) in Scheme 1. Within thefirst embodiment, the precursors (31), (33), and related precursors arethen used as shown in FIG. 2 to form the preliminary film. Within thefirst embodiment, as shown in FIG. 2, the preliminary film is then madeinto the final film using an energetic treatment step.

Within the second embodiment, the precursors (31) and (33) are convertedto a cyclic precursor or a prepolymer prior to forming the preliminaryfilm. Referring now to Scheme 2, precursor (31) wherein at least one ofR₁ or R₂ is R*, preferably an alkoxy, further transformed by acid orbase-catalyzed hydrolysis. Typically, the starting material is dissolvedin methylene chloride and treated with 0.1N aqueous HCl solution at 25°C. for 24 hrs. The volatiles are removed and the residue redissolved inmethylene chloride and dried over 4 Å molecular sieves. Higher dilutionsfavor the formation of cyclics when only two alkoxy substituents arepresent in the starting materials (K. Rahimian et al Chem. Mater. 2005,17, 1529).

Depending on the stereochemistry of the oxidative addition, reactionwith one equivalent of water can produce 2-oxa-1,3-disilylcyclopentanescontaining additional functionality for subsequent condensation, asshown in Scheme 2. Path A, producing precursor (35). This reaction,along Path A, occurs when the silane substituents are either rigidly cisor are freely rotating. In cases where cyclization does not occur,hydrolysis leads to polymerization and crosslinking as shown in Scheme2, Path B. This produces prepolymer (37). For monomers with multiplefunctionality (greater than two alkoxy groups), sol gel condensationoccurs with addition of more water.

Within a second embodiment of the present invention, the precursor (35),or the prepolymer (37), are then used as shown in FIG. 2 to form thepreliminary film. Within the second embodiment, as shown in FIG. 2, thepreliminary film is then made into the final film using an energetictreatment step described above.

Referring now to Scheme 3, a third embodiment within the invention isshown in which a related synthetic procedure is applied to norbornenesubstituted monomers. This embodiment builds a Si—C copolymer thatcontains subunits related to a successful organic porogen moleculebicycloheptadiene (norbornadiene). First precursor (39) is selected, andthe preliminary film contains the structure shown schematically as (41)formed by hydrolysis and condensation and is coated on the substrate. Instep (42), controlled heating causes the loss of the polycyclichydrocarbon fragments by retro Diels Alder reaction, forming a networkorganosilane containing bridging ethylene segments (43), a further stageof the preliminary film.

The steps of FIG. 2 which shows hydrolysis steps; in the above, thehydrolysis/condensation occurs in 3A, are applied. The double bonds in(43) are further incorporated into the final film and converted tosingle bonds during the energetic treatment step with UV curing beingpreferred.

An expanded list of candidate precursors is shown in Scheme 4, where thestructures of precursors (47)-(52) are shown. Scheme 4 is related toscheme 3, but with a broader selection of cyclic structures. All of thestructures except 51 are the result of Diels Alder cycloaddition ofbis-trialkoxysilyethylene (see 33) with the respective 1,3-diene.Reference numeral 51 is the product of oxidative addition of thehexaalkoxy disilane to beta pinene. These routes are generallyapplicable and the structures in Scheme 4 are representative of a largerset.

In (47)-(52), the cyclic hydrocarbon is the functionality R*, thebuilt-in sacrificial organic porogen group. This group is designed to bethermally labile or photoactive after sol gel processing forming thepreliminary film.

Above, the applicants have described examples where this thermallability has been introduced via retro Diels Alder chemistry or by thedecomposition of strained rings. Within the invention, the thermaldecomposition can be either by a single decomposition step or bystepwise thermal cascade. The end result is that a hydrocarbon moiety R*is removed during the energetic treatment Step 3 while retaining the twocarbon bridge between the silicon functionality in the final film.Ideally in this case the alkoxy substituents are either wholly or partlycomposed of substituents which are thermally labile either directly orin the presence of thermally generated acid (i.e., tertiary alkoxy,benzyloxy, benzhydryl, cyclopropyl carbonyl, tert-butylcarboxy and thelike).

According to the invention, in alternative embodiments, substituteddiborane molecules containing B—B bonding are used in place of thedisilane derivatives. The chemical schemes shown above in Schemes 1, 2,3 and 4 are applicable to the substituted diborane molecules within theinvention.

Scheme 5 shows a synthetic sequence to produce (by condensation) analkoxylated, hyperbranched carbosilane (63). The alkoxy substituentshere serve both as the source of condensation and crosslinking and asthe source of porosity from the formation of sacrificial groups. Thealkoxy groups in (63) are the R* group, within the fourth embodiment.The precursor shown in this scheme is then applied to a substrate andtreated as described above in forming the final dielectric film.

In addition to the above reactions, a thermal olefin generating reactionsuch as described in Schemes 6A-6G which can be used in the presentapplication. In each of the reactions Schemes 6A-6G olefin reactions areperformed which will cleave the side chains. This methodology representsan alternative to oxidative addition synthetic routes and the retroDiels-Alder routes mentioned above. Specifically, in these reactionspendant chains are eliminated by olefin forming reactions. In the olefinforming reactions the side chain becomes the pore generator. Schemes7A-7B describe the concept employed.

Specifically, Scheme 7A discusses the route for monomers containing onefunctional silicon, while Scheme 7B describes the application to thepreparation of carbosilane materials arising from monomers containingmore than one silicon/monomer unit. The initial step in each figure is asol-gel condensation to establish the polymer matrix. After the matrixis established, the final cure (thermal/photochemical) leads to completecuring of the organosilicate matrix material and the elimination of thelabile substituents to produce porosity. The loss of the labile materialis based on known elimination reactions to produce an olefin. For thisreason a tether is utilized to provide: (i) a link to silicon for thelabile substituent (ii) a scaffold for attaching the labile group to themolecule (iii) a structural unit for enabling the elimination. Theresult of this linkage is that an olefin unit remains attached tosilicon in the matrix after the labile group is removed. Thisfunctionality can be further incorporated into the matrix throughreaction. The linker in the manifestation described in Schemes 7A-7Bshould be at least two carbons in length and provide accessiblehydrogens for elimination, which often proceeds via a cyclic transitionstate. The size of the group eliminated determines the size of the poreleft behind and this can be tailored as desired. It is not necessarythat the labile substituent be attached via a flexible linker as long asa viable elimination pathway exits.

Scheme 8, for example, shows olefin formation within a cyclic systemwhere carbons bridge between two silicons. In Scheme 8, as shownpreviously in Schemes 7A-7B, the sol-gel matrix is established prior toelimination of the pore-generating group. The functionality left behindis still an olefin, albeit now one that is part of a cyclic systemwithin the matrix. Clearly, n-alkyl or cyclic systems would not berequired as long as hydrogens are accessible for elimination. It is wellknown that olefins are produced from the pyrolysis of esters, xanthates,amine oxides, quaternary ammonium salts, sulfones, sulfoxides andothers. The structural requirements are the functional group and thepresence of accessible hydrogens beta to the functionality (cyclictransition states). In the case of esters and ketones, a similarfragmentation also occurs photochemically (Norrish II). This may wellhappen for the other derivatives as well if the irradiation source is ofshort wavelength where light is absorbed. Depending on the substitutionpattern Norrish I fragmentation (alpha cleavage) can also befacilitated. These structural features can be incorporated into thelabile R* group. For the thermal reactions, all that is required arebeta hydrogens (i.e. a linker of at least two carbon atoms). Thefragmentation reactions produce the pores whose size depends on that ofthe R* group.

Scheme 8 describes a postcuring porosity sequence derived from oxidativeaddition of substituted disilanes to vinyl esters. Hydrolysis oftetraalkoxy derivatives will lead to both intra and intermolecularcondensation. Pyrolysis leads to beta elimination to produceunsaturation which can serve as an auxiliary matrix X-linking site. Inprinciple, the same procedure could be applied to alpha-beta unsaturatedesters, ketones, nitrites, etc. Again, photodecomposition is also apossibility.

In another embodiment of the present invention, a PECVD process is usedin forming the preliminary film. In the PECVD embodiment, any of theorganosilicon precursors described above including the built-in organicporogen R can be used. Using PECVD, the hydrolytic sol-gel condensationin Schemes 7A-7B and Scheme 8 is replaced with a matrix forming plasmadeposition process utilizing the alkoxy silane portion of the moleculein the same manner as is known in the art using commercial precursorssuch as diethoxymethylsilane (DEMS) and octamethyltetracyclosiloxane(OMCATS). Again, the porosity is predominately generated in a postdeposition cure. Preferably, the PECVD process uses a disilapropanederivative and the processing conditions described in U.S. applicationSer. No. 10/964,254, filed Oct. 13, 2004, the entire contents which areincorporated herein by reference, can be used in forming the preliminaryfilm.

Within the present invention, an organosilicon precursor molecule thatis preferably a disilapropane derivative is selected because theSi—CH₂—Si subunit in the precursor is then preserved in the finaldielectric film, and this improves the film interactions with water andwith plasma treatments occurring during integration.

Specifically, in this embodiment, the organosilicon precursor has thegeneral molecular formula R*R⁵R⁶Si—(CH₂)_(n)—Si—R⁷R⁸R⁹, where n is 1-2,R* is a sacrificial porogen group and R⁵⁻⁹ may or may not be identicaland are selected from H, alkyl, alkoxy, epoxy, phenyl, vinyl, allyl,alkenyl or alkynyl groups that may be linear, branched, cyclic,polycyclic and may be functionalized with oxygen, nitrogen or fluorinecontaining substituents. According to the present invention, thesacrificial organic porogen group R* is selected from one of groupsmentioned above for R*.

The present invention yet further provides for optionally adding anoxidizing agent such as O₂, N₂O, CO₂ or a combination thereof to form agas mixture including the organosilicon precursor, thereby stabilizingthe precursor in the reactor and improving the properties and uniformityof the porous dielectric material being deposited. Optionally, a flow ofa gas comprising one of CO, N₂, Ar, He, Ne, Xe or Kr may be added toimprove the film.

The method of the present invention may further comprise the step ofproviding a parallel plate reactor, which has an area of a substratechuck from about 85 cm² to about 750 cm², and a gap between thesubstrate and a top electrode from about 1 cm to about 12 cm. A highfrequency RF power is applied to one of the electrodes at a frequencyfrom about 0.45 MHz to about 200 MHz. Optionally, an additional RF powerof lower frequency than the first RF power can be applied to one of theelectrodes.

The conditions used for the deposition step may vary depending on thedesired final dielectric constant of the porous dielectric material ofthe present invention. Broadly, the conditions used for providing astable porous dielectric material comprising elements of Si, C, O, andH, and having a tensile stress of less than 60 MPa, an elastic modulusfrom about 2 to about 15 GPa, and a hardness from about 0.2 to about 2GPa include: setting the substrate temperature within a range from about100° C. to about 425° C.; setting the high frequency RF power densitywithin a range from about 0.1 W/cm² to about 2.0 W/cm²; setting theorganosilicon precursor flow rate within a range from about 10 mg/min toabout 5000 mg/min; optionally setting the inert carrier gases, such ashelium (or/and argon) flow rate within a range from about 10 sccm toabout 5000 sccm; setting the reactor pressure within a range from about1000 mTorr to about 10,000 mTorr; and setting the high frequency RFpower within a range from about 50 W to about 1000 W. Optionally, alower frequency power may be added to the plasma within a range fromabout 20 W to about 400 W. When the conductive area of the substratechuck is changed by a factor of X, the RF power applied to the substratechuck is also changed by a factor of X. When an oxidizing agent such asO2 is employed in the present invention, it is flowed into the reactorat a flow rate within a range from about 10 sccm to about 1000 sccm.

While liquid precursors are used in the above example, it is known inthe art that the organosilicon gas phase precursors can also be used forthe deposition.

In alternative embodiments, two or more organosilicon precursors areused, with one precursor providing Si—CH₂—Si bonding or Si—[CH₂]₂—Sibonding and the second precursor providing Si—O bonding. At least one ofthe two precursors contains a group R* which is as defined above.Methods according to the above embodiments are used, but with more thanone precursor.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A method of fabricating a SiCOH dielectric material comprisingforming a preliminary dielectric film containing at least oneorganosilicon precursor with a built-in sacrificial organic porogen on asurface of a substrate from a vapor or liquid phase, said at least oneorganosilicon precursor containing the built-in sacrificial organicporogen is selected from silane (SiH₄) derivatives having the molecularformula SiR*R¹R²R³, disiloxane derivatives having the molecular formulaR*R⁵R⁶Si—O—Si—R⁷R⁸R⁹, trisiloxane derivatives having the molecularformula R*R¹¹R¹²—Si—O—Si—R¹³R¹⁴—O—Si—R¹⁵R¹⁶R¹⁷ and disilaalkanederivatives having the molecular formula R*R⁵R⁶Si—(CH₂)_(n)—Si—R⁷R⁸R⁹,where n is 1-2, R* is a sacrificial porogen group and R¹⁻¹⁷, which mayor may not be identical, are selected from H, alkyl, alkoxy, epoxy,phenyl, vinyl, allyl, alkenyl or alkynyl groups that may be linear,branched, cyclic, polycyclic and may be functionalized with oxygen,nitrogen or fluorine containing substituents; and performing anenergetic treatment step on said preliminary dielectric film tosubstantially remove said built-in sacrificial organic porogen from saidpreliminary dielectric film providing a porous dielectric filmcomprising atoms of Si, C, H and O that has a dielectric constant ofabout 2.7 or less and a uniform and narrow and uniform pore sizedistribution.
 2. The method of claim 1 wherein the sacrificial porogengroup R* is selected from a branched alkyl, branched alkoxy, cyclicalkyl, cyclic alkoxy, aldehydes, ketones, esters, thioesters, amines,urethanes, triphenyl, alkyl phenyl carbinyl, substituted allyl,cyclohepatrienyl, cyclopropyl carbonyl, nitriles, azo derivatives, andalkyl groups which are connected to Si by a linker group.
 3. The methodof claim 2 wherein said linker group is thermally/photochemically labileor provides a platform to which labile substituents can be attached. 4.The method of claim 3 wherein said linker group is hydroxyethyl,hydroxypropyl, aminoethyl, aminopropyl, carboxyethyl, carboxypropyl, orbranched functional tethers.
 5. The method of claim 1 wherein said atleast one organosilicon precursor with the built-in sacrificial porogenis selected from the group consisting of molecules of the basic formula

wherein at least one of A, B or ring is the sacrificial organic porogenR*, and ring is also either one hydrocarbon ring containing a C—C unitbonded between two Si atoms or a polycyclic structure containing a C—Cunit between two Si atoms.
 6. The method of claim 1 wherein saidenergetic treatment step includes UV light, ionizing radiation, thermalenergy or a catalytic species.
 7. The method of claim 1 wherein saidpreliminary film contains a functional group selected from the groupconsisting of branched or cyclic hydrocarbon groups, polycyclichydrocarbon groups, branched or cyclic hydrocarbon groups bonded betweentwo or more Si atoms, polycyclic hydrocarbon groups bonded between twoor more Si atoms, acyl groups, ester groups, xanthate groups, amines,amine oxides, ethers, sulfonyl, sulfinyl, phosphate, phosphonyl,phosphinyl, organometallic and borate groups.
 8. The method of claim 1wherein said energetic treatment step releases molecules from thepreliminary film that are selected from the group consisting of linearor cyclic hydrocarbon fragments, olefins, acetylenes, alcohols, organicacids, amides, vinyl esters, xanthates, thioacids, amines,hydroxylamines, phosphines, phosphoric acids, phosphoric esters,substituted phosphonic, phosphinic esters, sulfonic acids, sulfinicacids, sulfides, mercaptans, nitrites and borates, and fragments of theaforementioned functional groups.
 9. The method of claim 1 wherein saidpreliminary dielectric film contains Si—CH₂—CH₂—Si bonding units. 10.The method of claim 1 wherein said forming said preliminary dielectricfilm comprises plasma enhanced chemical vapor deposition (PECVD) from avapor or spin-on application from a liquid.
 11. The method of claim 1wherein said preliminary dielectric film includes Si—CH₂—Si bondingunits.
 12. The method of claim 1 wherein said pore size distribution hasa maximum size pore of from about 0.1 to about 10 nanometers.
 13. Themethod of claim 1 wherein said pore size distribution is within thecross-hatched area of FIG.
 1. 14. A method of fabricating a SiCOHdielectric material comprising forming a preliminary dielectric filmcontaining at least one organosilicon precursor with a built-insacrificial organic porogen on a surface of a substrate from a vapor orliquid phase, said at least one organosilicon precursor containing thebuilt-in sacrificial organic porogen comprises a molecule of either:

wherein at least one of A, B or ring is a sacrificial organic porogenR*, and ring is also either one hydrocarbon ring containing a C—C unitbonded between two Si atoms or a polycyclic structure containing a C—Cunit between two Si atoms; and performing an energetically treatmentstep on said preliminary dielectric film to substantially remove saidbuilt-in sacrificial organic porogen from said preliminary dielectricfilm providing a porous dielectric film comprising atoms of Si, C, H andO that has a dielectric constant of about 2.7 or less and a uniform andnarrow and uniform pore size distribution.
 15. The method of claim 14wherein said preliminary dielectric film contains Si—CH₂—CH₂—Si bondingunits.
 16. The method of claim 14 wherein said forming said preliminarydielectric film comprises plasma enhanced chemical vapor deposition(PECVD) from a vapor or spin-on application from a liquid.
 17. Themethod of claim 14 wherein said pore size distribution has a maximumsize pore of from about 0.1 to about 10 nanometers.
 18. The method ofclaim 14 wherein said pore size distribution is within the cross-hatchedarea of FIG.
 1. 19. The method of claim 14 wherein R* is selected from abranched alkyl, branched alkoxy, cyclic alkyl, cyclic alkoxy, aldehydes,ketones, esters, thioesters, amines, urethanes, triphenyl, alkyl phenylcarbinyl, substituted allyl, cyclohepatrienyl, cyclopropyl carbonyl,nitriles, azo derivatives, and alkyl groups which are connected to Si bya linker group.
 20. The method of claim 19 wherein said linker group isthermally/photochemically labile or provides a platform to which labilesubstituents can be attached.